A vacuum insulation material includes a porous filler (core) and a barrier (barrier film) surrounding the filler, and has very low thermal conductivity by removing gas from the barrier film to maintain a vacuum for several years or more.
Insulation performance of the vacuum insulation material depends on the degree of vacuum therein and decreases as the internal vacuum degree is lowered. Thus, it is important to identify a defect of a product through evaluation of the internal vacuum degree of the vacuum insulation material.
In the related art, however, the degree of vacuum is evaluated based on thermal resistance obtained by converting heat flux and potential values on the surface of the vacuum insulation material.
Reliability of a vacuum evaluation method in the related art can vary according to sensitivity of a sensor for detecting heat flux and potential values and measurement conditions. In addition, in the vacuum evaluation method in the related art, since the degree of vacuum in the vacuum insulation material can be evaluated only in relation with thermal resistance instead of being directly evaluated, it is necessary to impart strong stress to the surface of the vacuum insulation material for a long period of time.